Ceramics are widely used for many industrial purposes. For example, ceramics such as steatite are used in the electronic and electrical appliance industries. The ceramics or porcelain can be formed into a great many sizes or shapes and can be used for grommets, bushings, washers, insulators, reostat bases, thermostat parts, etc. In addition, the ceramic may be used as a porcelain coating for metal substrates which are used in thick film ink circuitry. The term "steatite" may be used generically for the various forms thereof such as clinoenstatite, protoenstatite and enstatite. The latter, that is, enstatite, is the stable low-temperature form of steatite which, at a temperature of about 1040.degree. C. converts to protoenstatite, which is the stable high-temperature modification form. If protoenstatite is rapidly cooled to a temperature less than about 850.degree. C., a transformation of the protoenstatite occurs to form clinoenstatite which is the metastable low-temperature form of steatite. Generically speaking, the ceramic body is composed of magnesium silicate. If the magnesium and silicon are present in the ceramic in a mole ratio of 1:1, the compound may be designated as steatite, while if the magnesium and silicon are present in a mole ratio of 2:1 moles of magnesium per mole of silicon, the ceramic may be designated as forsterite.
When utilizing the ceramic as a coating for metal substrates in the electronic circuitry, it is necessary that the ceramic or porcelain possess certain desirable characteristics. The use of most ceramics and porcelains for coating metal substrates is limited by the particular conductive ink which is employed to form the circuitry. Most commonly, the inks which are employed with conventional porcelains are limited to those which require a fairly low temperature, that is, about 600.degree. C. to fire the ink. Additionally, the use of more reliable inks, that is, those which are fired at a temperature of about 850.degree. to 900.degree. C. is prohibited by the softening of conventional insulating porcelains at this firing temperature.
As will hereinafter be shown in greater detail, it has now been discovered that a steatite ceramic may be prepared by utilizing a particular process to obtain a ceramic which may be sintered to a high density ceramic at a relatively low temperature which will not adversely affect the metal substrate of a circuitry board, and will, in addition, permit the use of a reliable ink to form the desired circuitry.